Rotary compressor-expander systems and associated methods of use and manufacture, including two-lobed rotor systems

ABSTRACT

The present technology is directed generally to rotary displacement systems and associated methods of use and manufacture. The systems can be used to compress and/or expand compressible fluids. In some embodiments, the rotary displacement systems include a chamber housing having a pressure-modifying chamber with a first port and a second port, a first passageway in fluid communication with the chamber via the first port, and a second passageway in fluid communication with the chamber via the second port. The systems can further include a shaft positioned within the chamber housing and rotatable relative to the chamber housing about a rotational axis, and a rotor comprising no more than two lobes. The rotor can be carried by and rotatable relative to the shaft, and can be alternately operable in a first mode in which flow is provided from the first passageway to the second passageway via the chamber and in a second mode in which flow is provided from the second passageway to the first passageway via the chamber.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority to and the benefit of U.S.Provisional Patent Application No. 61/309,415, filed on Mar. 1, 2010 andtitled UNDERWATER COMPRESSED AIR ENERGY STORAGE, which is incorporatedherein by reference in its entirety.

TECHNICAL FIELD

The present technology is directed generally to rotarycompressor-expander systems, e.g., for compressing, storing, and/orreleasing compressed fluids.

BACKGROUND

Power demand from an electric system can vary considerably. In order toimprove the efficiency of an electric system, it is desirable to storeexcess, off-peak, and renewably-generated electricity so that the storedelectricity can be utilized when demand is high. There are severalavailable methods for storing energy which is later used to produceelectricity, including batteries, elevated hydro systems, and compressedair energy storage (CAES) systems.

CAES systems compress atmospheric air in a compressor driven by energyfrom the electric system. The compressed air is stored in a compressedair reservoir, e.g., a geological formation or other structure. When theenergy is demanded, the compressed air can be heated and expanded togenerate electricity. Various devices can be used to compress and expandthe air for the CAES system. For example, a positive displacementmachine (PDM), such as a typical internal combustion engine,reciprocating air compressor, or rotary displacement device, cancompress air for storage. One of the cost reduction methods for CAESsystems is to use a PDM in a bidirectional manner for both thecompression and expansion processes. However, bidirectional PDMs areoften mechanically complicated and tend to operate at high pressureratios, causing high temperature changes in the system. This can resultin a relatively low amount of recovered energy. As a result, thereexists a need for an efficient, low-cost, bidirectional (e.g.,reversible) compressor/expander for use in a CAES system.

BRIEF DESCRIPTION OF THE DRAWINGS

Many aspects of the present disclosure can be better understood withreference to the following drawings. The components in the drawings arenot necessarily to scale. Instead, emphasis is placed on illustratingclearly the principles of the present disclosure. Moreover, in thedrawings, like reference numerals designate corresponding partsthroughout the several views.

FIG. 1 is a partially schematic illustration of a compressed air energystorage system configured to store and release compressed fluids inaccordance with several embodiments of the present disclosure.

FIG. 2 is a partially schematic front view of a two-lobed rotarydisplacement system configured in accordance with an embodiment of thedisclosure.

FIG. 3 is a partially schematic front view of a three-lobed rotarydisplacement system configured in accordance with an embodiment of thedisclosure.

FIG. 4A is a front isometric view of a compressor/expander systemconfigured in accordance with embodiments of the disclosure.

FIGS. 4B-4E are schematic views of the compressor/expander system ofFIG. 4A at representative points during operation.

FIG. 5 is an enlarged end view of an upper portion of the system 310shown in FIG. 3.

FIG. 6A is a partially schematic isometric view of a rotary displacementsystem having an integral heat exchanger configured in accordance withan embodiment of the disclosure.

FIG. 6B is a partially schematic, isometric side view of a multi-stagerotary displacement system having an integral heat exchanger configuredin accordance with another embodiment of the disclosure.

FIG. 6C is a partially schematic isometric end view of an interiorportion of the system of FIG. 6B.

FIG. 6D is a partially schematic isometric end view of the system ofFIG. 6B.

FIG. 7 is a front view of a rotary displacement system having aninsulator configured in accordance with an embodiment of the disclosure.

FIG. 8 is a partially schematic isometric view of a rotary displacementsystem having a generally hollow rotor configured in accordance with anembodiment of the disclosure.

FIG. 9 is a partially schematic isometric view of a rotary displacementsystem having a plurality of rotors operating in parallel in accordancewith an embodiment of the disclosure.

FIG. 10 is an exploded side isometric view of a rotary displacementsystem configured in accordance with another embodiment of thedisclosure.

FIG. 11 is an isometric view of a rotary displacement system configuredin accordance with an embodiment of the disclosure.

DETAILED DESCRIPTION

The present technology is directed generally to a rotarycompressor-expander system for storing and releasing compressed fluids,and associated systems and methods. In at least some contexts, thesystem includes a pressure-modifying chamber, valveless fluidcommunication between the chamber and first and second passageways, anintegral heat exchanger, and/or a rotor having three or fewer lobes(e.g., two lobes). In several embodiments, the rotor is capable ofoperating bidirectionally, e.g., in a first configuration or mode inwhich flow is provided from the first passageway to the secondpassageway via the chamber, and in a second configuration or mode inwhich flow is provided from the second passageway to the firstpassageway via the chamber. In other embodiments, the technology andassociated systems and methods can have different configurations, modes,components, and/or procedures. Still other embodiments may eliminateparticular components or procedures. A person of ordinary skill in therelevant art, therefore, will understand that the present technology mayinclude other embodiments with additional elements, and/or may includeother embodiments without several of the features shown and describedbelow with reference to FIGS. 1-11.

Some or all of the foregoing features have particular applicability andadvantages in the context of renewable energy sources. In particular,many renewable energy sources (e.g., solar and wind) provide energy in amanner that varies significantly with time. Combined compressor/expandersystems in combination with a suitable reservoir provide an efficientmechanism by which to store energy and release energy at a later time.By improving the efficiency with which such compressor/expander systemsoperate, aspects of the presently disclosed technology can improve theefficiency with which energy from renewable sources is obtained, storedand used.

Many embodiments of the technology described below may take the form ofcomputer-executable instructions, including routines executed by aprogrammable computer. Those skilled in the relevant art will appreciatethat aspects of the technology can be practiced on computer systemsother than those shown and described below. The technology can beembodied in a special-purpose computer or data processor that isspecifically programmed, configured or constructed to perform one ormore of the computer-executable instructions described below.Accordingly, the terms “computer” and “controller” as generally usedherein refer to any data processor and can include Internet appliancesand hand-held devices (including palm-top computers, wearable computers,cellular or mobile phones, multi-processor systems, processor-based orprogrammable consumer electronics, network computers, mini computers andthe like). Information handled by these computers can be presented atany suitable display medium, including a CRT display or LCD.

The technology can also be practiced in distributed environments, wheretasks or modules are performed by remote processing devices that arelinked through a communications network. In a distributed computingenvironment, program modules or subroutines may be located in local andremote memory storage devices. Aspects of the technology described belowmay be stored or distributed on computer-readable media, includingmagnetic or optically readable or removable computer disks, as well asdistributed electronically over networks. Data structures andtransmissions of data particular to aspects of the technology are alsoencompassed within the scope of the technology.

Overview

FIG. 1 schematically illustrates a representative overall system 100 forstoring energy generated at one time for use at a later time. Theoverall system 100 can include one or more energy supply sources 102which supply energy in the direction of arrow A toward an energy storagedevice (e.g., a reservoir) 108, via electrical lines on a power grid104. The supplied energy can be generated from a number of suitablesources, including, for example, wind, solar, natural gas, oil, coal,hydro, nuclear, and/or others.

A power device 106 (e.g., a motor, generator or motor/generator) usesenergy from the supply source 102 to electrically or mechanically drivea bi-directional compressor/expander 110 to operate in a firstconfiguration or mode. In the first mode, the compressor/expandercompresses a fluid, e.g., atmospheric air. Heat generated duringcompression may be dissipated or retained for later use in an expansionprocess. After the air has been compressed, the air is directed toward acompressor/expander fluid storage volume 101 of the energy storagedevice 108.

The energy storage device 108 can include a geological formation,underwater compressed fluid storage vessels, a high-pressure tank,and/or other suitable volume. In some embodiments, the energy storagedevice 108 is an underwater device as described in U.S. ProvisionalPatent Application No. 61/309,415, UNDERWATER COMPRESSED AIR ENERGYSTORAGE, which has been incorporated by reference herein. In someembodiments, the energy storage device 108 includes thecompressor/expander fluid storage volume 101 and a thermal storagevolume 103. The compressor/expander fluid storage volume 101 can storeworking fluid processed by the bi-directional compressor/expander 110.The thermal storage volume 103 can store heated or cooled fluid used bythe bi-directional compressor/expander 110 or by other processes ormachines.

When energy consumers 112 demand additional energy from the grid 104,the energy storage device 108 can supply compressed air or another fluidto the bidirectional compressor/expander 110 which operates in a secondmode to expand the compressed air or other fluid. In some embodiments,heat can be added to the compressor/expander 110 during the expansionprocess. The heat can be a product of the compression process or cancome from another heat source (e.g., a warm liquid reservoir, exhaustfrom a gas turbine, and/or other suitable sources). Expanding air in thecompressor/expander 110 drives the power device 106 to supplyelectricity to the grid 104 in the direction of arrow B. The electricityis thus provided to the energy consumers 112. The compressor/expander110 can operate at various speeds based on energy demand and otherfactors. In some embodiments, for example, the compressor/expander 110operates at a low speed, producing a low amount of power, but at a highefficiency. In other embodiments, the compressor/expander 110 operatesat a higher speed, producing a higher amount of power, at a lowerefficiency.

The system 100 can also include a controller 148 that directs theoperation of one or more system components, e.g., the power device 106,the compressor/expander 110 and/or the energy storage device 108.Accordingly, the controller 148 can receive inputs 117 (e.g., sensorinputs) and direct outputs 119 (e.g., control signals) via computerimplemented instructions. For example, the controller 148 can receiveinputs corresponding to energy levels produced by the supply source 102and demanded by the consumers 112 and, based on the differences betweenthese levels, control the direction of fluid flow through thecompressor/expander 110, e.g. to direct fluid through thecompressor/expander 110 into the energy storage device 108 when theenergy supply exceeds demand, and reverse the fluid flow when demandexceeds supply. In some embodiments the controller 148 can be responsiveto operator input or other factors, in addition to or in lieu ofresponding to supply and demand levels.

FIG. 2 is a partially schematic front view of a two-lobed rotarydisplacement system 210 configured in accordance with an embodiment ofthe disclosure. The system 210 can include a first fluid passageway 214,a second fluid passageway 216, and chamber housing 218 having an innerwall 220 and an outer wall 222. The first fluid passageway 214 can haveworking fluid at a first pressure and the second passageway 216 can haveworking fluid at a second pressure higher or lower than the firstpressure. The chamber housing 218 at least partially surrounds apressure-modifying chamber 224. In a particular embodiment shown in FIG.2, the pressure-modifying chamber 224 is generally circular, but inother embodiments can have a modified oval, oblong, trochoidal, or othercurved shape. The pressure-modifying chamber 224 can further include afirst port 226 connecting the first passageway 214 to thepressure-modifying chamber 224 and a second port 228 connecting thesecond passageway 216 to the pressure-modifying chamber 224.Accordingly, the first and second ports 226, 228 extend through thechamber housing 218. In several embodiments of the present disclosure,there is no valve between the pressure-modifying chamber 224 and thefirst passageway 214 and/or between the pressure-modifying chamber 224and the second passageway 216, as will be discussed in further detaillater.

In several embodiments of the disclosure, the system 210 includes abidirectional compressor/expander, configured to operate as a compressorin a first mode and an expander in a second mode. Depending on theoperational mode of the system 210 (e.g., whether it is being run as acompressor or an expander), the first port 226 operates as an inlet portor an outlet port and the second port 228 performs the oppositefunction, e.g., it operates as an outlet port or an inlet port. Forexample, in a first mode, in which the system 210 is running as acompressor, the rotor 232 rotates in a first direction, the first port226 functions as an inlet port (feeding low-pressure working fluid, orflow, into the compression chamber 224), and the second port 228functions as an outlet port (accepting compressed working fluid andfeeding it to the first passageway 214). In the second mode, in whichthe system is running as an expander, the rotor 232 rotates in a seconddirection opposite the first direction, the first port 226 operates asan outlet port, the second port 228 operates as an inlet port, and thedirection of flow through the system 210 is reversed. In otherembodiments, the system 210 operates as a dedicated compressor orexpander, and does not run bidirectionally. In particular embodiments,the system 210 can have more than two ports. For example, in someembodiments, the system 210 can have two inlet ports and two outletports. The ports 226, 228 can be rectangular with rounded corners orotherwise shaped. The ports 226, 228 are positioned in the chamberhousing 218 in manners that differ in different embodiments of thedisclosure, as will be described in further detail later. In any ofthese embodiments, individual ports (e.g., the first port 226 and thesecond port 228) are separated from each other by a separation portion230 of the chamber housing 218.

The system 210 can further include a rotor 232 coupled to andeccentrically rotatable relative to a shaft 234 which runs through acenter portion 236 of the rotor 232. An eccentric cam 268 is furthercoupled to the shaft 234 and is positioned in the center portion 236 ofthe rotor 232. The rotor 232 can have a plurality of lobes 238. Whilethe rotor 232 illustrated in FIG. 2 includes two lobes 238, in otherembodiments it can have three or more lobes. The lobes 238 can havevarious shapes, curvatures, and dimensions in different embodiments ofthe disclosure. In general, each lobe 238 extends radially outwardlyfrom the center 236 of the rotor 232 by a greater amount than do theneighboring regions of the rotor 232, so that a peripheral boundary 233of the rotor 232 is non-circular. Each lobe has a tip 239 at theradially-outermost point of the lobe 238. The shaft 234 extends into(e.g., traverses) the chamber 224 along a rotational axis R_(A) normalto the plane of FIG. 2. The shaft 234 can be electrically and/ormechanically connected to a motor, a generator, or a motor/generator(shown schematically in FIG. 1). The rotor 232 is actuated by rotatingthe shaft 234 and the cam 268. The rotation direction of the shaft 234determines the rotation direction of the rotor 232 and whether thesystem 210 is operating as a compressor or expander. As will bediscussed in further detail below with reference to FIG. 3, gears can beadded in some embodiments to effect rotor rotation.

In the illustrated embodiment, both the first port 226 and the secondport 228 are radially positioned. In other words, the ports 226, 228 arepositioned on a surface 221 of the chamber housing 218 that is generallyparallel to the rotational axis R_(A). As the rotor 232 makes orbitalrevolutions around the shaft 234, the lobe tips 239 rotate past thefirst and second ports 226, 228 and cyclically cover and uncover thefirst and second ports 226, 228.

Seals (e.g., tip rollers 240) on the lobes 238 seal the rotor 232against the inner wall 220 of the chamber housing 218. The tip rollers240 can be generally cylindrical and are mounted to the lobes 238 via aroller-mount 241, such as a gear-free wheel-and-axle apparatus or aspherical wheel system. The rollers 240 can be forced against the rotorwalls in a modulated manner by springs or other pressure devices (e.g.,as disclosed in U.S. Pat. No. 3,899,272), to provide low-frictioncontact with the chamber housing inner wall 220, and can also guide therotor position. The rollers 240 can also help ensure that pressurizedfluid does not escape from a chamber zone 242 bounded by the rotor 232and the housing inner wall 220. In other embodiments, other tip-sealingfeatures, such as sliding seals, liquid films, and/or a purposefullyplaced gap space between the lobe 238 and the inner wall 220 of thechamber housing 218 can be used. In one embodiment, for example, a thinfilm of liquid can be applied to the chamber housing 218 or the lobetips 239. In some embodiments, the thin film can comprise seawater,freshwater, oil, glycol, glycerin, and/or another material, or acombination of materials. The thin film can provide a higher flowresistance across a gap between the tip 239 and the chamber housinginner wall 220. In other embodiments, air bearings can be applied to thetip 239 to seal the chamber zone 242 with minimal friction. In at leastsome embodiments, the inner wall 220 of the pressure-modifying chamber224 and/or portions of the rotor 232 can include one or morelow-friction coatings 244. The coating 244 can include plastic, ceramic,or other materials. In low-temperature applications, a low-frictioncoating (e.g., Teflon, epoxy, polycarbonate, cross-linked polyethylene,and/or other material) can improve the integrity of the seal, whileproviding relatively low friction between the rotor 232 and the chamber224 and without incurring the expense of a high temperature seal.

The separation portion 230 between the first port 226 and the secondport 228 can carry a seal, e.g., a variable geometry seal 246. Thevariable geometry seal 246 can engage with the peripheral boundary 233of the rotor 232 as the rotor 232 eccentrically rotates in the chamber224. The variable geometry seal 246, in combination with the rotorperiphery 233 and rollers 240 contacting the inner wall 220 of thechamber housing 218, divides the chamber 224 into individual chamberzones 242 having individual zone pressures. In the illustrated position,the chamber 224 has only one chamber zone 242 due to the orbitalorientation of the rotor 232. Rotating the rotor 232 alters the size andnumber of the zones 242, as will be discussed in further detail belowand with reference to FIGS. 4A-4E.

The orbital position of the rotating rotor 232 with respect to thechamber housing inner wall 220 can determine the size of the chamberzones 242 and the pressure of the fluid within the zones 242. Forexample, the rotor 232 illustrated in FIG. 2 is oriented in theequivalent of a bottom dead center position. In the compression mode,the rotor 232 rotates in a first rotation direction (e.g., clockwise)about the eccentric shaft 234 to deliver compressed working fluid to ahigh-pressure passageway (e.g., the second passageway 216). In theexpansion mode, the rotor 232 rotates in the opposite direction todeliver expanded working fluid to a low-pressure passageway (e.g., thefirst passageway 214). As discussed above with reference to FIG. 1, thesystem 210 can include a controller 148 to control the rotationdirection of the rotor 232, which in turn determines whether the system210 operates to compress or expand. The controller 148 may accordinglyreceive inputs 117 (e.g., from sensors and/or an operator) and provideoutputs 119 to direct the rotor 232. The controller 148 can redirect therotation of the rotor 232 by mechanical, electrical, electromechanicaland/or other suitable devices. For example, in several embodiments thecontroller 148 controls the rotation direction and torque of the shaft234. In some embodiments, the controller 148 can perform functions inaddition to controlling the bidirectionality of the system 210. In anyof these embodiments, the controller 148 can include any suitablecomputer-readable medium programmed with instructions to direct theoperation of the system 210.

The system 210 can further include a heat exchanger 258 positionedoutside the chamber housing 218. The heat exchanger 258 can include aheat exchanger passageway 256 in fluid communication with one or more ofthe first and second passageways 214, 216 and/or the chamber 224. In oneembodiment, a heat exchanger housing wall 261 positioned between theheat exchanger passageway 256 and the first and/or second passageways214, 216 channels flow between the heat exchanger passageway 256 and thefirst and/or second passageways 214, 216. Flow can be channeled toenhance working fluid contact with the heat exchanger 258. The heatexchanger 258 can be dedicated to providing heating or cooling, or canbe bidirectional so as to cool fluid processed by the chamber 224 duringcompression and add heat during expansion. In other embodiments, fluidis injected directly into the chamber 224 and/or a passageway 214, 216,or 256 by one or more nozzles 231, such as an atomizing spray nozzle.The injected fluid can be colder or hotter than the working fluid in thechamber 224, and can accordingly cool or heat the working fluid inaddition to or in lieu of the heat transfer effect provided by the heatexchanger 258. Further aspects of the heat exchanger 258 will bediscussed later with reference to FIGS. 6A-6D.

An outer housing 250 can at least partially surround or encase thechamber housing 218, the first passageway 214, and the second passageway216. The outer housing 250 can have an inwardly facing inner surface 252and an outwardly facing outer surface 254. The outer housing 250 can beradially spaced apart from the chamber housing 218, providing room forthe passageways 214, 216, 256, the heat exchanger 258, stabilizingfeatures 260 (e.g., standoffs), an insulator material (not shown in FIG.2, but discussed in further detail later with reference to FIG. 7),and/or other components. In FIG. 2, the outer vessel 250 is illustratedas being generally cylindrical, but in other embodiments can be othershapes and/or can only partially surround the chamber housing 218. Theouter housing 250 can be axially adjacent to one or more bulkheads 262.In the illustrated embodiment, only one axial bulkhead 262 is shown soas to not obscure the inner-workings of the system 210, but in otherembodiments the outer housing 250 can be sandwiched between two axialbulkheads 262. In this manner, the outer housing 250 and the bulkheads262 can form a pressure vessel for the flow within the system 210.Accordingly, the inner surface 252 of the outer housing 250 and thebulkheads 262 contact and/or contain pressurized flow passing throughthe system 210. Using the outer housing 250 as a pressure vessel canreduce the material requirements for the overall system 210.

As mentioned above, the inner surface 220 of the chamber housing 218 canhave one or more coatings 244 to reduce friction and/or manage wear. Thecoating 244 can be applied to other surfaces of the system 210 (inaddition to or in lieu of the inner surface 220), e.g., other surfacesof the chamber housing 218, the outer housing 250, the rotor 232, thepassageways 214, 216, the fluid passageways 256, the heat exchanger 258,the bulkheads 262 and/or the shaft 234, in order to achieve desiredfunctional or material characteristics such as heat resistance orcorrosion resistance. For example, when the system 210 is used forcombustion engine applications, high-temperature coatings, such asceramics, can be used to protect the surfaces from hot fluids. In lowtemperature compressor applications, plastic coatings can be used toimprove corrosion resistance and reduce friction at lower cost.

FIG. 3 is a partially schematic front view of a three-lobed rotarydisplacement system 310 configured in accordance with another embodimentof the disclosure. The system 310 includes many features that werediscussed above with reference to FIG. 2, including a chamber housing218 having an inner surface 220 and an outer surface 222, acompression/expansion chamber 224, a rotor 332, a shaft 234, and anouter housing 250 having an inner wall 252 and an outer wall 254. Thesystem 310 further includes first and second passageways 214, 216 andfirst and second ports 226, 228 connecting the passageways 214, 216 tothe chamber 224. In the illustrated embodiment, there are four ports,but in other embodiments the system 310 can include more or fewer ports.In several embodiments, there are no valves in the ports 226, 228 orbetween the passageways 214, 216 and the chamber 224.

A ring gear 366 (e.g., a planetary gear) is disposed on the innerperiphery of a central portion 336 of the rotor 332 and is positioned tomesh with a pinion 364 disposed on the outer periphery of the shaft 234.An eccentric cam 368 is mounted on the shaft 234 and is positioned inthe center portion 336 of the rotor 336. The rotor gear 366 meshes withthe pinion 264 to eccentrically orbit the rotor 332 around the chamber224. In other embodiments, other mechanisms, such as the cam describedabove with reference to FIG. 2, rotate the rotor 332 without the needfor gears.

In the illustrated embodiment, the rotor 332 has a rotor periphery 333that is generally triangular, comprising three curved lobes 338. Eachlobe 338 has a tip 339, and each tip 339 has a tip-widener feature 370.In other embodiments, the rotor 332 can have more or fewer than threelobes 338 and the lobes 338 can have different degrees of curvature. Thetip wideners 370 radially and circumferentially extend from the lobetips 339 and contact the inner wall 220 of the chamber housing 218. Thewideners 370 divide the chamber 224 into multiple (e.g., three) chamberzones 342. The lobes 338 and tip wideners 370 of the turning rotor 332cyclically cover and uncover the first and second ports 226, 228. Thelocation of the rotating rotor 332 with respect to the chamber housinginner wall 220 determines the sizes of the chamber zones 342 and thecorresponding flow pressures within the zones 342. In some embodiments,the tip wideners 370 can be attached to fewer than every lobe 338 or maybe absent altogether. The tip wideners 370 will be discussed in furtherdetail later with reference to FIG. 5.

The preceding overview introduced several systems and methods forefficiently and effectively compressing and expanding fluids in varioussettings. For example, in an underwater CAES system with high externalpressures and high fluid volume, embodiments of bidirectionalcompressor/expanders with three or fewer lobes and large ports canprovide for a high flow of fluid with low fluid friction. The largeports are made possible by various designs and features, e.g., the tipwideners and the variable geometry seals introduced above and describedin further detail below.

Several of the systems described above can reduce or minimize operationand/or material costs while improving efficiency. For example, in someembodiments the compressor/expander can be placed in proximity to alarge body of water that provides a constant source of heat or coolingenergy. Additionally or alternatively, the body of water can provide arepository for water warmed by the compression process. If the warmedwater is contained, the warmed water can later be used during theexpansion process, using the same heat exchange method used to collectthe heat of compression. Furthermore, the reduced lobe designs generallyrequire less mass and thus less cost for the volume of gas that theycompress. Valveless, bidirectional operation of the compressor/expandercan offer further efficiency and can reduce device complexity andmaterial costs. The following sections describe several of thesefeatures and advantages in more detail and will introduce additionalrelated features and advantages.

Two-Lobed Rotor

FIG. 4A is a front isometric view of a compressor/expander system 410configured in accordance with an embodiment of the disclosure. Thesystem 410 includes several features generally similar to thosedescribed above with reference to FIGS. 2 and 3. For example, the system410 includes a rotor 232 carried by and rotatable relative to a shaft234, with the rotor 232 and the shaft 234 positioned within apressure-modifying chamber 224 which is at least partially surrounded bychamber housing 218. The rotor comprises two lobes including a firstlobe 238 a and a second lobe 238 b. The chamber housing 218 has an innerwall 220 and an outer wall 222. The chamber 224 includes a first port226 and a second port 228 which connect the chamber to low- andhigh-pressure passageways (not shown). In several embodiments, there areno valves in the ports 226, 228 or between the ports and thepassageways.

The system 410 can further include a variable geometry seal 246slideably coupled to a portion 230 of the chamber housing 218 betweenthe first port 226 and the second port 228. The variable geometry seal246 can include an internal spring 447 to bias the variable geometryseal 246 into engagement with a peripheral boundary 243 of the rotor 232as the rotor 232 eccentrically rotates in the chamber 224. The variablegeometry seal 246 can maintain a continuous sealing engagement with theperiphery 233 of the rotor 232 by radially reciprocating between aforward position in which the variable geometry seal 246 extends intothe compression/expansion chamber 224 and a retracted or recessedposition in which the variable geometry seal 246 is generally flush withan inner wall 220 of the chamber housing 218. In a particular aspect ofthis embodiment, a first portion of the variable geometry seal 246 canbe fixed relative to the chamber housing 218 while a second portion canbe radially and/or circumferentially moveable relative to the chamberhousing 218. For example, the seal 246 can include a seat that is fixedrelative to the chamber housing 218, and a sealing surface that moves(e.g., radially reciprocates) relative to the chamber 218. The variablegeometry seal 246, in combination with the rotor 232 pressing againstthe chamber inner wall 220 (e.g., via the roller 240), creates one ormore chamber zones (e.g., three zones) 442 identified individually aszones 442 a-442 c in FIGS. 4A-4E. In at least some embodiments, thesystem 410 can include multiple variable geometry seals 246.

The rotor 432 illustrated in FIG. 4A includes tip rollers 240. Asdiscussed above with reference to FIG. 2, the rollers 240 can decreasethe friction between the rotor lobes 238 and the inner wall 220 of thechamber housing 218 and between the rotor lobes 238 and the variablegeometry seal 246. The rollers 240 can also better enable the rotor 232to follow the contours of the chamber housing 218.

FIGS. 4B-4E are schematic views of the compressor/expander system 410shown in FIG. 4A, at representative points during operation. Referringfirst to FIG. 4B, the rotor 232 is positioned to cover the first andsecond ports 226, 228. A first chamber zone 442 a contains a fluid andin this position of the rotor's orbit, the volume of the first zone 442a is maximized. As the rotor 432 turns approximately 45°counter-clockwise as indicated by arrow R and shown in FIG. 4C,low-pressure fluid enters a second zone 442 b via the first port 226.The volume of the first zone 442 a has decreased, compressing the fluidin the first zone 442 a. The spring 447 coupled to the variable geometryseal 246 pushes the variable geometry seal 246 radially inward to remainengaged with the rotor periphery 233.

An interstitial zone 442 c is formed between the variable geometry seal246 and the approaching first lobe 238 a. The interstitial zone 442 c isfilled with high-pressure fluid via the second port 228, but in someembodiments this small volume of fluid will simply discharge from thesecond port 228 with low losses as the first lobe 238 a approaches thevariable geometry seal 246. In some embodiments, the system 410 includesgrooves (not visible in FIG. 4C) in the inner wall 220 of the chamberhousing 218 between the variable geometry seal 246 and the second port228, thus allowing the interstitial volume 442 c to be vented into ahigh-pressure passageway at any rotor position.

In FIG. 4D, the rotor 232 has continued to rotate in a counterclockwisedirection. In this position, the fluid in the first zone 442 a has beencompressed to the desired pressure ratio and begins discharging into ahigh-pressure passageway via the second port 228. The first lobe 238 ais at the edge of the second port 228. Low-pressure fluid continues tofill the second zone 442 b.

In FIG. 4E, the rotor 232 has continued to rotate counterclockwise andin this position, fluid on one side of the rotor 232 discharges from thechamber 224 while fluid on the other side enters the chamber 224.Specifically, pressurized fluid in the first zone 442 a (at a desiredpressure ratio relative to the incoming fluid) discharges via the secondport 228. Low-pressure fluid continues to fill the second zone 442 b. Byselecting the size and spacing of the ports 226, 228, the designer canobtain the desired pressure ratio, which can be different for differentembodiments of the system. The rotor 232 then continues to rotate to theposition shown in FIG. 4B, but now with the second zone 442 b filledwith fluid and the first and second lobes 238 a, 238 b in oppositepositions.

The foregoing sequence was described in the context of a representativecompression mode. It will be understood that the rotor 432 can rotate inthe opposite direction to expand the fluid in an expansion mode. Asdescribed above, the change between compression and expansion modes canbe controlled by the controller 148 (shown schematically in FIG. 2).

One feature of the foregoing arrangement is that the pressure ratiobetween the ports 226, 228 can be designed to be modest, e.g. on theorder of 1.2 in particular embodiments. An advantage of the arrangementis that it reduces the temperature increase during compression, whichallows the system to be manufactured with relatively low temperaturematerials. This in turn can reduce the overall cost of the systems. Whenit is necessary to compress the fluid by a greater pressure ratio (as istypically the case), the system can include multiple stages arranged inseries, as described later with reference to FIG. 6B. Another feature ofthe foregoing arrangement is that it includes a rotor with only twolobes. An advantage of this feature is that it can allow greaterflexibility in positioning and/or sizing the first and second ports.This in turn can facilitate larger ports which can improve theefficiency of the system, as described, further later.

Tip Wideners

FIG. 5 is an enlarged end view of an upper portion of the system 310shown in FIG. 3. The system 310 has several features generally similarto those described above with reference to FIGS. 2 and 3. For example,the system 310 includes a chamber housing 218 surrounding apressure-modifying chamber 224. The chamber 224 has a first port 226 anda second port 228 connected to a first passageway 214 and a secondpassageway 216, respectively. As discussed above, there are no valvesbetween the ports and the passageways in at least some embodiments. Thesystem 310 further includes an outer housing 250 surrounding thepressure-modifying chamber 224 and the passageways 214, 216. A rotor 332having a lobe 338 with a tip 339 is positioned in the chamber 224. Theillustrated portion of the system 310 highlights a tip widener 370 thatcan be moveably coupled to the lobe tip 339.

The tip widener 370 can include independently flexing arms 592 a and 592b that are forced radially outwardly, e.g., by a torsion spring (notvisible in FIG. 5) located at an attachment point 594 and/or by theresilient structure of the arms 592 a, 592 b. The arms 592 a, 592 b canbe independently flexible so as to continuously contact the varyingangles along an inner wall 220 of the chamber housing 218 as the rotor332 rotates. For example, the tip widener 370 can comprise a resilientlybendable, pre-formed material, such as a plastic or spring steel. Inother embodiments, the tip widener 370 can have more or fewer than twoarms 592 a, 592 b and can tend radially outwardly under a force otherthan a spring force. The tip widener 370 can be attached to the lobe 338by a number of suitable mechanisms, including, for example, welding,frictionally securing, gluing, and/or fasteners.

In still further embodiments, the tip widener 371 can be mounted to thelobe 338 at an attachment point 594 that includes a pivot joint so as topivot relative to the lobe 338, as indicated by arrow P. In thisembodiment, the tip widener 370 can be flexible, as discussed above, ormore rigid. If it is more rigid, it can be positioned on a slot 595 soas to translate toward and away from the inner wall 220 (as indicated byarrow T) as it pivots.

The tip widener 370 can have a circumferential extent C₁ that is largerthan a circumferential extent C₂ of the first and second ports 226, 228.In other words, when the tip widener 370 is positioned over anindividual port, the tip widener arms 592 a, 592 b effectively seal theport from fluid communication with the chamber 224. Accordingly, the tipwideners 370 can decrease the circumferential spacing required betweenthe input and output ports 226, 228. Using the three-lobed rotor 332 asan example, the spacing between conventional lobe tips is approximately120°, resulting in ports that need to be fairly evenly spaced around thecircumference of the housing. However, the tip widener 370 allows theports 226, 228 to be placed at points less than 120° apart, in effectincreasing the circumferential spread of the lobe 338. This flexibilityof port placement allows for greater displacement efficiency of thedevice 310. The circumferential extent C₁ of the tip widener 370 canvary depending on the number and spacing of the ports 226, 228 and thedesired timing of port openings and closings. The circumferential extentC₁ of the tip widener 370 can vary to provide the desiredcircumferential space between lobes 338. For example, in one embodimenthaving four ports, three lobes, and a pressure ratio of 1.4, thecircumferential extent between each proximate pair of high pressure andlow pressure ports can be approximately 89°, the circumferential extentbetween tip wideners can be approximately 51°, the opening sizes of thelow pressure ports can be approximately 28°, and the opening sizes ofthe high pressure port can be approximately 17.5°.

Both the tip wideners and the variable geometry seals can significantlyreduce reverse flow conditions while still accommodating large portsizes. For example, the tip wideners can reduce or minimize reverse flowby effectively narrowing the effective circumferential spacing betweenports along the inner wall of the chamber. Likewise, variable geometryseals dynamically separate high- and low-pressure sides of the chamber,reducing the chance that high- and low-pressure ports will besimultaneously open within a single zone. By reducing reverse flowconditions and accommodating large ports, the system can benefit fromreduced tip bypass flow and allows port opening and closing timing to beoptimized, thereby improving system efficiency. While these featureswere described above in the context of a three-lobed rotor, they can beapplied alone or in combination to a two-lobed rotor.

Large Ports

As discussed above, several embodiments of the disclosed systems includeport sizes that are significantly larger than existing ports withoutcreating overly large reverse flow conditions. For example, in variousrepresentative two lobe design arrangements with pressures ratios fromabout 8 to about 1.2, ports can be sized to be from about 3% to about15% or more of the circumference of the chamber inner surface withoutthe system encountering large reverse flow conditions during operation.In various representative three lobe arrangements with pressure ratiosfrom about 8 to about 1.2, ports can be sized to be from about 4% toabout 15% of the circumference of the chamber inner surface withoutencountering large reverse flow conditions in operation. These largeports can be enabled by the variable geometry seal and/or the tipwidening features.

Integral Heat Exchanger

FIG. 6A is a partially schematic isometric view of a rotary displacementsystem 610 a having an integral heat exchanger 658 a configured inaccordance with an embodiment of the disclosure. The system 610 aincludes several features generally similar to those described abovewith reference to FIGS. 2 and 3. For example, the system 610 a includesa chamber housing 218 having an inner wall 220 and an outer wall 222, apressure-modifying chamber 224, a rotor 332 rotatably coupled to a shaft234, first and second passageways 214, 216, and first and second ports226, 228 in the chamber 224 providing fluid communication between thechamber 224 and the individual passageways 214, 216.

The heat exchanger 658 a is positioned radially outside the chamberhousing 218 and the passageways 214, 216. The heat exchanger 658 aincludes one or more heat exchanger supply tubes 659 which convey aheated or cooled heat exchanger fluid. In the illustrated embodiment,the heat exchanger 658 a surrounds a portion of the chamber housing 218and is in fluid communication with working fluid from thepressure-modifying chamber 224. Specifically, working fluid exiting thechamber 224 via the second port 228 flows radially outwardly in thedirection of arrows F₁ through the second passageway 216, and into aheat exchanger passageway 256 to make contact with the heat exchanger658 a. The working fluid exchanges heat with the heated or cooled heatexchanger fluid in the supply tube 659.

The system further comprises an outer housing 250 (a portion of which isshown in FIG. 6A) having an inner surface 252 and an outer surface 254.The outer housing 250 can at least partially surround and/or encase thechamber housing 218, the pressure-modifying chamber 224, the passageways214, 216, and the heat exchanger 658 a. In several embodiments,pressurized working fluid passing through the heat exchanger 658 acontacts the inner surface 252 of the outer housing 250, which acts as apressure vessel to contain the working fluid. Using the interior of theouter housing 250 as a pressure vessel eliminates the need for severalpipe-fittings and passageways between the pressure-modifying chamber 224and the ports 226, 228, the passageways 214, 216, and the heat exchanger658 a, and between one stage and the next in multi-stage systems.

The heat exchanger 658 a illustrated in FIG. 6A is a finned-tube heatexchanger. Other embodiments can include other types of heat exchangerssuch as shell-and-tube heat exchangers, plate heat exchangers,gas-to-gas heat exchangers, direct contact heat exchangers, fluid heatexchangers, phase-change heat exchangers, waste heat recovery units, orother types of heat exchangers. For example, in some embodiments, theheat exchanger 658 a can comprise a waste heat recovery unit (not shown)that transfers heat from a hot gas stream to the heat exchange fluid.The hot gas stream can be an exhaust gas stream from a gas turbine or adiesel engine, or a waste gas stream from a refinery, or otherindustrial system.

The heat exchanger fluid can comprise freshwater, seawater, steam,coolant, oil, or other suitable gaseous liquid and/or biphasic fluids.The heat exchanger 658 a can operate in both the compression andexpansion modes to support a bidirectional compressor/expander, and mayinteract with the compressed/expanded flow before or after the flowenters the chamber 224. In some embodiments, the heat exchanger fluid isthe same for both the compression and expansion modes of operation ofthe device, while in other embodiments different heat exchanger fluidsare used. In some embodiments, heat exchanger fluid that is heatedduring operation in the compression mode can be stored, e.g., in anexterior thermal storage reservoir for use during operation in theexpansion stage. The heat exchanger 658 a can be made of a number ofsuitable materials or combinations of materials, including metals,ceramics, or plastics. In several embodiments, the heat exchanger is atleast partially made of corrosion-resistant materials (e.g. copper,cupro-nickel, titanium, stainless steel and others) in order to allowfor the use of a wide variety of heat exchange fluids.

As will be discussed in further detail below with reference to FIG. 6B,multiple pressure-modifying chambers 224 (e.g., stages) can be fluidlyconnected and can operate in series. In some multi-stage embodiments,the radial heat exchanger 658 a axially extends along the outer wall 222of multiple chamber housings 218. In such an embodiment, thecompressed/expanded working fluid travels radially outwardly from afirst port 228 of a first stage (as indicated by arrows F₁), into theheat exchanger 658 a, axially along the heat exchanger 658 a, and thenradially inwardly to enter a second port of a second pressure-modifyingchamber (not shown). When the system operates in the compression mode,the working fluid can be cooled between stages. When the system operatesin the expansion mode, the working fluid can be heated between stages.Interstage heating and cooling can reduce (e.g., minimize) thetemperature changes between stages that can rob the system 610 a ofoperating efficiency. By directing the working fluid in the passageways214, 216 radially outwardly from the chamber housing 218 the system canreduce pressure oscillations between stages and allow for significantheat exchanger length.

FIG. 6B is a partially schematic, isometric side view of a multi-stagerotary displacement system 610 b having multiple integral heatexchangers 658 b in accordance with another embodiment of thedisclosure. The system 610 b includes multiple stages (numberedindividually as stages 672-675) axially aligned along a shaft 234. Forpurposes of clarity, the rotors carried by the shaft 234 are not shownin FIG. 6B. Each stage can include a chamber housing 218 having firstand second ports 226, 228, a first passageway 214, and a secondpassageway 216. Each stage 672-675 can additionally include one or morebulkheads 662 positioned axially adjacent to the corresponding chamberhousing 218.

The system 610 b further includes multiple axial heat exchangers 658 baxially aligned between compression/expansion stages 672-675. The heatexchangers 658 b are in fluid communication with working fluid in thefirst and/or second passageways 214, 216. Specifically, the workingfluid travels from one stage to the next in the direction of arrows F₂.For example, the working fluid can exit a first stage 672 through acorresponding second port 228 and then flow axially into an axiallyadjacent heat exchanger 658 b. The working fluid then enters the firstport 226 of the adjacent stage 673 and the process is repeated as theworking fluid travels from right to left in FIG. 6B. In someembodiments, the working fluid travels directly from the secondpassageway 216 into the heat exchanger 658 b and in other embodimentsthe working fluid traverses through one or more apertures in theadjacent bulkhead 662 (discussed in further detail below with referenceto FIG. 6C) and then into the adjacent heat exchanger 658 b. The workingfluid transfers thermal energy in the heat exchanger 658 b and continuesaxially into the first passageway 214 and first port 226 of the adjacentsecond stage 673. The first port 226 and second port 228 of sequentialstages may be offset clockwise or counterclockwise relative to eachother in order to better direct the working fluid through the system 610b.

Like the radial heat exchanger 658 a discussed above with reference toFIG. 6A, the axial heat exchanger 658 b can operate in both compressionand expansion modes to support a bidirectional compressor/expander. Anyof the types of heat exchangers and heat exchanger fluids describedabove can be used in the axial heat exchanger 658 b as well. While threeheat exchangers 658 b and four compression/expansion stages 672-675 areillustrated in FIG. 6B, other embodiments can include more or fewerstages and/or heat exchangers 658 b, and the arrangement of the stages672-675 and heat exchangers 658 b can vary. For example, a multi-stageddesign can be used in systems not having an integral heat exchanger.Furthermore, the axial length of the compression/expansion stages672-675 and the heat exchangers can vary within a system 610 b. Forexample, differing axial lengths can be used to maintain generallyconsistent pressure ratios from one stage to the next due to thechanging density of the working fluid from stage to stage.

Referring now to FIG. 6C, the system 610 b can further includeperforated bulkheads 662 having reinforcing ribs 684. An individualbulkhead 662 includes one or more apertures 682 that allows the workingfluid to flow into the passageways and corresponding chamber ports of anadjacent stage. In embodiments for which the outer housing and bulkheads662 act as a pressure vessel for the working fluid passing through thesystem 610 b, the bulkheads 662 can experience a significant bendingforce from the internal pressure, particularly around the apertures 682located near the periphery of the bulkhead 662 where the bulkhead 662 iscoupled to the outer housing. Accordingly, the reinforcing ribs 684 canbe welded or otherwise affixed across the apertures 682 to prevent orlimit bulkhead deformation due to internal pressure, while stillallowing fluid flow to the internal heat exchanger 658 b. While thereinforced ribs 684 are illustrated on a system 610 b having an axialheat exchanger 658 b, they can be used in embodiments having a radialheat exchanger (e.g., the heat exchanger 658 a shown in FIG. 6A) or inembodiments having no heat exchanger.

Turning now to FIG. 6D, the system 610 b can further include adistribution plate 686 positioned between an individualpressure-modifying chamber 224 and the adjacent heat exchanger 658 b.The distribution plate 686 can span all or a portion of thepressure-modifying chamber 224 and can include a plurality of openings685. The distribution plate 686 is positioned to disseminate workingfluid over the heat exchanger 658 b more effectively. Specifically, asthe working fluid exits the second port 228 in a radial direction, itpasses circumferentially around the outside of the chamber 224, asindicated by arrows C₃ and then axially through the openings 685 andthrough the heat exchanger 658 b. In various embodiments, the openings685 on the distribution plate 686 can have different sizes and shapes,the distribution plate 686 can have more or fewer openings 685, and/orthe openings 685 can be arranged in other configurations. The plate 686can accommodate working fluid flowing in either direction, asappropriate for a bidirectional compressor/expander system. While thedistribution plate 686 is illustrated in the context of a system 610 bhaving an axial heat exchanger 658 b, an analogous plate can be usedwith a radial heat exchanger similar to that depicted in FIG. 6A. Forexample, the distribution plate 686 can be curved to match the curve ofthe heat exchanger, and can be positioned radially between a passagewayand a corresponding radial heat exchanger. Furthermore, while the rotor332 is illustrated as a three-lobed rotor 332, in other embodimentsintegral heat exchanger designs and/or multi-stage designs can be usedwith rotors having more or fewer (e.g., two) rotor lobes.

Radial and axial heat exchangers can be used separately or incombination in rotary displacement systems. Dimensional characteristicscan influence which type of integral heat exchanger to use in aparticular system. For example, axial heat exchangers provide fornarrow, lengthened, systems while radial heat exchangers provide forwider, but shorter systems which require fewer inter-stage bulkheads (astwo adjacent stages can share a common divider bulkhead). Regardless ofwhat type of heat exchanger is chosen, integrating the heat exchangerinto the device can provide for more constant temperature operation ofthe rotary displacement device. In bidirectional systems, the integralheat exchanger allows for efficient restoration of the heat producedduring compression to the expansion cycle. In compressed air energystorage applications, the use of integral heat exchangers cansignificantly improve the round-trip energy efficiency of air betweenthe compressor/expander and the energy storage system and can reduceoperating costs by reducing or eliminating the natural gas typicallyrequired to add heat during the expansion process.

Fluid injection can additionally or alternatively be used to exchangeheat in rotary displacement devices. As introduced with reference toFIG. 2, fluid injection comprises introducing an injection fluid(typically a liquid) to the pressure-modifying chamber 224 to cause athermal transfer between the fluid and the flow within the chamber 224.In some embodiments, the injection fluid can include seawater, freshwater, oils (such as vegetable oil or mineral oil), or refrigerants suchas a fluorocarbon. The selection of injection fluid can depend on anumber of injection fluid characteristics, including, for example, theinjection fluid's surface tension, specific heat, heat transfercoefficient, costs to atomize the injection fluid, lubricativeproperties, and environmental friendliness. In several embodiments, theinjection fluid is non-combustible and/or is specifically selected to beinjected into chamber 224 or other region without combusting.

In various embodiments, the fluid can be introduced via the first port226, via one or more separate fluid-delivery ports in the chamberhousing, and/or via one or more fluid ports in the rotor (discussed infurther detail below with reference to FIG. 8). In other embodiments,the injection fluid is introduced in the first or second passageways214, 216 or in the heat exchanger passageway 256. In still furtherembodiments, injection fluid is introduced from multiple locations toprovide more even injection fluid distribution into the pressure-variedfluid. In several embodiments, the injection fluid is introduced via anozzle (shown schematically in FIG. 2) such as an atomizing spraynozzle. In some embodiments, the injection fluid is atomized to increasesurface area and injection fluid suspension in the working fluid. In oneembodiment, for example, the injection fluid is about 500 microns orsmaller. In a particular embodiment, the injection fluid is atomized tobe sized from about 20 to about 100 microns. Upon injection, theinjection fluid can absorb heat of compression or can provide heat forexpansion by direct contact with the working fluid in the chamber. Insome embodiments, the heat exchange injection fluid may be injected intothe gas stream prior to either expansion or compression, or the gasstream may be allowed to percolate through the heat exchange fluid. Insome embodiments, feedback from one or more temperature sensorsmonitoring either the working fluid or injection fluid outputtemperature can be used by the controller, possibly along withinformation about the thermal energy storage and other parameters, toadjust the quantity of liquid and the method of injection to achievevarious objectives which may include a high efficiency of operation or adesired temperature range.

The injection fluid can be extracted via the discharge port 228 with thepressure-modified fluid or it can be separately extracted with variousmechanisms such as sump-like devices, condensation (such as condensationoff a heat exchanger 658 a or 658 b), centrifugal separation, or baffleplates in passageways 214, 216, 256. Upon extraction, the heat-exchangeliquid can be stored in a thermal reservoir. In some embodiments theinjection fluid may go through a liquid-to-liquid heat exchanger whichwill either extract heat from the fluid after compression or provideheat to the fluid prior to expansion. Depending on the desired operatingconditions and the relative mass flow and specific heat of the liquid,liquid injection may eliminate or reduce the need for a separate heatexchange mechanism. Fluid injection heat exchange can be inexpensive andcan allow for closer approach temperatures between the working fluid andthe injection fluid. A number of liquids can be used for liquidinjection heat exchange, including any of those mentioned above withreference to FIGS. 6A-6D. Additionally, in some embodiments, fog (e.g.,a suspension of liquid droplets or condensed vapor) can be used as theheat exchange fluid.

One feature of the foregoing heat exchangers is that they can re-useheat generated at one location in the system and/or during one mode ofoperation in another portion of the system and/or during another mode ofoperation. This arrangement can enhance the overall thermodynamicefficiency of the system and can thereby reduce the cost of operatingthe system. In particular embodiments, the heat can be exchanged betweenthe rotary displacement device and the ambient environment, or aseparate thermal reservoir, or both. Generally, the greater thetemperature rise permitted in the exchange fluid, the greater theadvantage of storing the heat for later retrieval.

Insulation

FIG. 7 is a front view of a rotary displacement system 710 having aninsulator 798 configured in accordance with an embodiment of thedisclosure. The system 710 includes several features generally similarto those described above with reference to FIGS. 2 and 3. For example,the system 710 includes a chamber housing 218 having a first passageway214 and a second passageway 216 and surrounding a pressure-modifyingchamber 224 and a rotor 232 carried by and rotatable relative to a shaft234. The system also includes a heat exchanger 258 and an outer housing250 having an inner surface 252 and an outer surface 254.

In a particular embodiment, the insulator 798 is positioned radiallyoutside the outer housing 250. In the illustrated embodiment, theinsulator 798 circumferentially contacts and surrounds the outer surface254 of the outer housing 250, but in other embodiments may surround onlya portion of the outer housing 250. In other embodiments, the insulator798 can be internal to the outer housing 250 and can contact the innersurface 252 of the outer housing 250. In still further embodiments, theinsulator 798 can contact the chamber housing 224, the heat exchanger258, and/or a passageway 214, 216 and the outer housing can be absent orradially outward of the insulator 798. The insulator 798 can include anouter shell that is spaced apart from the outer housing by an air gapor, as illustrated, the gap can be filled with a suitable insulatingfiller material 797. In some embodiments, the filler material 797 can befiberglass filler or other materials. In other embodiments, the gap canbe evacuated to provide an insulating effect. In any of theseembodiments, the insulator 798 can contribute to maintaining fluidtemperatures within the system 710, particularly within the integralheat exchanger 258.

Hollow Rotor

FIG. 8 is a partially schematic isometric view of a rotary displacementsystem 810 having a generally hollow rotor 832 configured in accordancewith an embodiment of the disclosure. The system 810 includes severalfeatures generally similar to those described above with reference toFIGS. 2 and 3. For example, the system 810 includes an outer housing250, a chamber housing 218, and a pressure-modifying chamber 224.

In the illustrated embodiment, an end surface of the rotor 832 is cutaway to illustrate that the rotor 832 has a generally hollow interiorportion 891 framed by rotor walls 890. In some embodiments, for example,only a small portion of the volume of the rotor 832 comprises rotorwalls 890, leaving the rest of the rotor 832 at least partially, and insome embodiments predominantly, hollow. In one embodiment, for example,the rotor walls 890 comprise five percent or less of the rotor volume.In some embodiments, the rotor walls 890 can be locally thickened tobalance the rotor as it spins. In other embodiments, the rotor walls 890may be made of more than one layer of material stiffened with ahoneycomb structure or filler separating the layers.

The rotor 832 can include various internal features. In one embodiment,the rotor interior 891 includes a stiffening structure 888 to addsupport to the rotor 832 structure. The stiffening structure 888 canalso include a center structure 836 for mating with the shaft and cam.For example, as discussed above with reference to FIG. 3, the centerstructure 836 can support the ring gear 366. The rotor 832 canadditionally or alternately include internal cavities 889. In oneembodiment, an internal cavity 889 is filled with filler material toachieve a desired rotor 832 weight. In another embodiment, as describedabove with reference to FIG. 6, the internal cavity 889 includes aninternal fluid passageway 889 and an output port 883 for supplying heatinjection fluid to the pressure-modifying chamber 224 as a method ofheat exchange.

In some embodiments, the rotor 832 can be cast or fabricated from platematerials. For example, in one embodiment, the rotor 832 can befabricated from cut, formed, and welded plate materials. While the rotor832 illustrated in FIG. 8 is a two-lobed rotor 832, in other embodimentsthe rotor 832 can have three or more lobes.

One feature of the hollow rotor 832 is that is can be easily fabricated,inexpensive, and lightweight. Accordingly, the hollow rotor 832 canreduce the cost and complexity of the system in which it is installed.Another feature of the hollow rotor 832 is that it can reduce eccentricloading on the shaft due to inertial accelerations. Accordingly, it canreduce fatigue loads and therefore increase the life of the systems inwhich it is installed.

Parallel Rotors

FIG. 9 is a partially schematic isometric view of a rotary displacementsystem 910 having a plurality of rotors 932 (e.g., three) operating inparallel in accordance with an embodiment of the disclosure. The system910 includes several features generally similar to those described abovewith reference to FIGS. 2 and 3. For example, the system 910 includes achamber housing 218, a pressure-modifying chamber 224, and a shaft 234.The chamber housing 218 is illustrated as transparent in FIG. 9 forpurposes of clarity, but in several embodiments the chamber housing 218is not transparent. The three rotors 932 operate in parallel within thechamber housing 218. The rotors 932 can share a common first port 226and a common second port 228 which each run axially along the chamberhousing 218. The rotors 932 can further share common first and secondpassageways (not shown in FIG. 9). The system 910 further comprisesbulkheads (which have been hidden for purposes of clarity) axiallypositioned between each rotor 932, so that each rotor 932 is positionedin a separate chamber 224.

The rotors 932 can be offset clockwise or counterclockwise relative toeach other, so that each rotor 932 is positioned in a different orbitallocation within its chamber 224 at a given moment. Operating the offsetrotors 932 in parallel offers several advantages. For example, theoffset angles of the rotors 932 can balance the torque on amotor/generator that is coupled to the shaft 234. Specifically,vibrations and shaft-bending loads that arise from the eccentric motionof a single rotor 932 are balanced by the counter-movement of theadditional rotors 932. Additionally, the offset angles further limitpressure oscillations in the first and second passageways by averagingthe intake and discharge pulsations across rotors operating at differentphase angles and also by increasing the volume in these flow channels.The higher volume in the flow channels reduces the risk that there willbe an undesirably high discharge pressure or an undesirably low intakepressure. As discussed above, discharge from one stage can be timed tocoincide with the intake of the next stage, which can smooth the overallflow and avoid undesirable pressure oscillations.

Construction Techniques

FIG. 10 is an exploded side isometric view of a rotary displacementsystem 1010 configured in accordance with another embodiment of thedisclosure. The system 1010 is constructed using a “ring and plate”technique that reduces construction costs and materials. The method ofconstruction includes forming a chamber housing 1018 and an outerhousing 1050 into cylindrical sections. This can be done by variousmethods, including rolling and welding a plate material or by forgingthe material into the cylindrical shape. Port openings 1026 can bepre-cut into the plate material used to form the chamber housing 1018.Standoffs 1045 can be formed or coupled to the chamber housing 1018 tocreate separation between passageways in the resulting system 1010.

In some embodiments, the method can include coating one or more of thematerials or structures, e.g., the heat exchanger, the distributionplate, the chamber housing 1018, and/or the outer housing 1050. Forexample, in some embodiments, the method can include flame-sprayingcoatings, such as plastic, onto structural materials, such as steel, forcorrosion resistance. In other embodiments, dry lubricants such asmolybdenum sulfide or graphite can be applied. Additionally oralternatively, low friction coatings such as Teflon, epoxy, orpolycarbonate, may be applied to certain surfaces. In other embodiments,one or more elements of the system 1010 can be coated with a ceramicmaterial. The method can further include axially aligning a shaft 234, arotor 332, the chamber housing 1018, and the outer housing 1050. Theshaft, rotor, and chamber housing 1018 radially nest within the outerhousing 1050. In some multi-stage embodiments, the shaft 234 comprisesseveral segmented portions which are mated with separable joints, suchas male-female spline features or pinned socket joints. In particularembodiments, the shaft can be hollow.

Once the rotor 332, the shaft 234, and the chamber housing 1018 areaxially aligned within the outer housing 1050, the method can furthercomprise positioning a first bulkhead 1062 a on a first axial side 1053of the outer housing 1050 and positioning a second bulkhead 1062 b on asecond axial side 1055 of the outer housing 1050. In some embodiments,the first and second bulkheads 1062 a, 1062 b have first and secondbulkhead diameters, respectively, with the first and second bulkheaddiameters greater than a diameter of the outer housing 1050 and/or adiameter of the chamber housing 1018. The bulkheads 1062 a, 1062 b caninclude one or more flow apertures 682, as discussed in more detailabove with reference to FIG. 6C.

The method of construction can additionally include connecting the firstbulkhead 1062 a to the second bulkhead 1062 b with a plurality oftension members 1096 (identified as multi-part tension members 1096 a,1096 b, and 1096 c), thereby securing the outer housing 1050 between thefirst bulkhead 1062 a and the second bulkhead 1062 b and enclosing aninternal pressurizable volume. The tension members 1096 can compriserods and bolts, latches, fasteners, and/or other connectors. In someembodiments, the tension members 1096 secure the first bulkhead 1062 ato the second bulkhead 1062 b radially exterior to the outer housing1050. The bulkheads 1096 can additionally be sealed to the outer housing1050. In other embodiments, the outer housing 1050 can be absent and thebulkheads 1062 can be positioned on first and second axial sides of thechamber housing 1018. In the case of multi-stage structures, adjacentstages can share a common bulkhead, with gasket seals between axialstages to assist carrying internal pressure loads. Gasket or o-ringseals compressed by the tension members 1096 can create robust andremovable joints. Furthermore, the bulkheads 1062 can be welded orsealed to at least one of the chamber housing 1018 or outer housing1050.

Embodiments of the ring-and-plate construction offer several advantages,including easy assembly and disassembly, and quick and directmaintenance access to the interior cavities. Another feature of thedesign is that it can be modular. For example, different stages can usethe same or similar common parts, reducing production and machiningcosts. A multi-stage system similar to that illustrated in FIG. 6B canincorporate identical bulkheads having identical perforations andshaft-openings for multiple stages. In some embodiments, stage lengthscan differ in order to maintain a similar pressure ratio from one stageto the next and to compress or expand air in small increments. Despitediffering stage lengths, the same tools and assemblies can be used toform the chamber housing and the outer housing cylinders of differentstages. Using the modular design described above, the number of stagescan be easily adjusted.

Brayton Cycle

While many rotary displacement devices discussed above have beendescribed in the context of bidirectional compressor/expander systems,the features and methods disclosed herein can be used in dedicatedcompressors and dedicated expanders as well. FIG. 11 is an isometricview of the interior of a rotary displacement system 1110 having adedicated compressor 1176 and a dedicated expander 1177 configured inaccordance with an embodiment of the disclosure. The system 1110 isconfigured for use as a Brayton cycle heat engine, in which the workingfluid is compressed as a gas, heated, and then expanded. The system 1110includes a dedicated compressor 1176, a heat supply 1178, and adedicated expander 1177 in axial alignment along a shaft 234. Thecompressor 1176, heat source 1178, and expander 1177 can fluidlycommunicate through perforated bulkheads 262 or other types of fluidpassageways. In some embodiments, the system 1110 comprises multiplestages of compressors and/or expanders.

The individual compressors 1176 and expanders 1177 can include any ofthe features described herein. For example, the illustrated compressor1176 includes a compression chamber 1179 having input and dischargeports (not visible in FIG. 11), a two-lobed rotor 232 rotatably coupledto the shaft 234, a low-pressure passageway 1116, a high-pressurepassageway 1114, a heat exchanger 1158, and an outer housing 250. Thecompressor 1176 is configured to introduce flow from low-pressurepassageway 1116 into the compression chamber 1179 where the fluid iscompressed and then discharged into a high-pressure passageway 1114. Theheat exchanger 1158, integral to the compressor 1176, can be similar tothose described above with reference to FIGS. 6A-6D and, in amulti-stage compressor, can cool the flow between stages, furtherincreasing the efficiency of the compression process. In someembodiments, the system 1110 is connected to a thermal distributionsystem, or fluid distributor (not shown), configured to distribute heatgenerated during compression for space conditioning (e.g., heating andheat-driven cooling). In other embodiments, the compressor 1176 can havealternate features, such as a three-or-more-lobed rotor, a variablegeometry seal, tip wideners, an axial heat exchanger, or other features.

The heat source 1178 can vary from one embodiment to another. Forexample, the heat source 1178 in the illustrated embodiment comprises aplurality of combustion chambers 1181. In other embodiments, the heatsource 1178 may be a single combustion chamber. The heat source can usesolid fuels, such as biomass or coal, liquid fuels, such as gasoline ordiesel, or gaseous fuels, such as natural gas or hydrogen. In anotherembodiment, the heat source 1178 can comprise one or more heatexchangers, e.g., any of the types of heat exchangers described a movewith reference with FIGS. 6A-6D above. For example, the heat source 1178can include a “waste heat recovery” heat exchanger with heat exchangerfluid heated by the exhaust of an automobile engine or power plant gasturbine. Other embodiments may comprise more than one type of heatsource, such as a heat exchanger followed by a combustion chamber. Insome embodiments, the heat source 1178 shares a common outer housingwith the compressor and the expander. The heat source outer housing isnot shown in FIG. 11 for purposes of clarity.

The expander 1177 can be structurally similar or identical to thecompressor 1176, except the expander 1177 is configured to introduceflow from a high-pressure passageway into an expansion chamber where thefluid is expanded and then discharged into the low-pressure passageway.An integral expander heat exchanger can heat the flow between stages ina multi-stage expander. In some embodiments, the expander 1177 has alonger axial length L_(E) than a compressor axial length L_(C) toaccommodate the increased volume of heated flow. In the illustratedembodiments the compressor 1176, heat supply 1178, and expander 1177 areaxially aligned but in other embodiments they may be radially orotherwise oriented. Furthermore, in various embodiments the compressor1176, heat supply 1178, and/or expander 1177 can share a common shaft234 or have separate shafts.

The various embodiments of rotary displacement devices disclosed hereinoffer numerous benefits, some of which have been discussed above withreference to particular features. The two- and three-lobed embodimentsutilize various mechanisms (e.g., the variable geometry seal and/or thetip wideners) to eliminate the need for a check valve between thepressure-modifying chamber and the passageways. The systems can reduceor eliminate reverse flow conditions and the time that neither port isopen. These mechanisms can also reduce system cost and complexity, whichin turn reduces initial system cost and subsequent maintenance costs.The foregoing arrangement can also allow the systems to more quickly anddynamically alternate between the compression and expansion modes.Furthermore, the relatively large port sizes in several of the devicesreduce pressure losses through the intake and exhaust ports, againincreasing the overall efficiency of the device.

Several of the construction techniques disclosed herein offer costsavings over conventional techniques. Some of these include reducingmaterial requirements, improving material durability via coating,sharing parts and production methods, effective use of waste heat, andreduced assembly and disassembly time. Combining the compressor andexpander in a single efficient structure and using the same internalcomponents, such as a common heat exchanger, for each mode of operationsignificantly reduces system costs over devices having separatecompressors and expanders. Furthermore, several of the devices disclosedherein can operate directly coupled to an electric motor via a shaft.This reduces or eliminates costs associated with gearboxes, and reducesthe overall technical complexity of the system.

The foregoing features can be particularly advantageous in the contextof a compressor/expander system that is used to both store and releaseenergy, as shown in FIG. 1. In particular the foregoing features canreduce the cost of storing and releasing energy supplied by sources thatmay provide energy on an intermittent, non-continuous or other variablebasis. For example, several renewable energy services (e.g., solarenergy and wind energy) typically provide energy in a highly variablemanner. Systems and methods that reduce the cost of using such energysources efficiently and effectively can create significant benefits,including reducing the use of fossil fuels and therefore reducing globalwarming and dependence on foreign energy sources.

From the foregoing, it will be appreciated that specific embodiments ofthe technology have been described herein for purposes of illustration,but that various modifications may be made without deviating from thetechnology. For example, several features of the disclosure arediscussed in the context of a bidirectional rotary displacement system.Many of these features, including tip-wideners, variable geometry seals,integral heat exchangers, hollow rotors, construction techniques,materials, and chamber/rotor geometry can be applied in the context ofsystems that are not bidirectional. In particular embodiments, these andother features can be applied to dedicated compressor or expandersystems and/or to systems having other features generally similar tothose described herein. In particular embodiments, some or all of thefeatures can be used in the context of two-lobed rotors and/or rotorshaving more than two lobes, multistage systems, and/or parallel intakeand output arrangements, with or without integral heat exchangers.

Certain aspects of the technology described in the context of particularembodiments may be combined or eliminated in other embodiments. Forexample, some embodiments may not include one or more of the followingfeatures: tip rollers or other sealing features, tip wideners, avariable geometry seal, multiple stages, material coatings,ring-and-plate construction techniques, a hollow rotor, or otherfeatures disclosed herein. Further, while advantages associated withcertain embodiments have been described in the context of thoseembodiments, other embodiments may also exhibit such advantages and notall embodiments need necessarily exhibit such advantages to fall withinthe scope of the present technology. Accordingly, the present disclosureand associated technology can encompass other embodiments not expresslydescribed or shown herein.

1. A rotary displacement system comprising: a chamber housing having apressure-modifying chamber with a first port and a second port; a firstpassageway in fluid communication with the chamber via the first port; asecond passageway in fluid communication with the chamber via the secondport; a shaft positioned within the chamber housing and rotatablerelative to the chamber housing about a rotational axis; and a rotorpositioned within the pressure-modifying chamber and comprising no morethan two lobes, wherein the rotor is carried by and rotatable relativeto the shaft, and wherein the rotor is alternately operable in a firstmode in which flow is provided from the second passageway to the firstpassageway via the chamber and in a second mode in which flow isprovided from the first passageway to the second passageway via thechamber.
 2. The system of claim 1 wherein no valves are positioned tocontrol flow (a) between the chamber and the first passageway and (b)between the chamber and the second passageway.
 3. The system of claim 1,further comprising a seal positioned between the first port and thesecond port and having a varying radial extent to sealably contact thelobes of the rotor as the rotor rotates.
 4. The system of claim 1,wherein the rotor includes a first rotor, the pressure-modifying chamberincludes a first pressure-modifying chamber, and wherein the systemfurther comprises a second rotor positioned within a secondpressure-modifying chamber, wherein: the first rotor has a first rotororientation, the second rotor has a second rotor orientation, and thefirst rotor orientation is offset clockwise or counterclockwise from thesecond rotor orientation; the second rotor comprises no more than twolobes; the second rotor shares the first passageway and the secondpassageway with the first rotor; and the second rotor is carried by theshaft and rotatable relative to the shaft in parallel with the firstrotor.
 5. (canceled)
 6. The system of claim 1, further comprising avariable geometry seal positioned between the first port and the secondport, wherein: at least one of the first port and the second port ispositioned in a surface of the chamber housing that is generallyparallel to the rotational axis; no valves are positioned to controlflow (a) between the chamber and the first passageway and (b) betweenthe chamber and the second passageway; and the rotor and the variablegeometry seal divide the pressure-modifying chamber into chamber zones,wherein an individual chamber zone is in communication with only one ofthe first passageway and the second passageway at a given point in time.7. The system of claim 6 wherein each rotor lobe includes a lobe tip,and wherein the system further comprises a tip-sealer positioned betweenthe chamber housing and an individual lobe tip, the tip sealercomprising at least one of a rolling cylinder, a thin film of liquid,and a low-friction coating.
 8. (canceled)
 9. The system of claim 1,further comprising: a fluid storage reservoir in fluid communicationwith the first and second passageways; an electric motor/generatorcoupled to the shaft; and a controller coupled to the shaft and operableto redirect the rotor between operation in the first mode and the secondmode by reversing a rotation direction of the shaft.
 10. A rotarydisplacement system comprising: a chamber housing having apressure-modifying chamber with a first port and a second port; a firstpassageway in fluid communication with the chamber via the first port; asecond passageway in fluid communication with the chamber via the secondport; a shaft positioned within the chamber housing and rotatablerelative to the chamber housing about a rotational axis; a rotor carriedby and rotatable relative to the shaft and having a rotor periphery; anda variable geometry seal coupled to the chamber housing between thefirst port and the second port and sealably engaged with the rotorperiphery.
 11. The system of claim 10 wherein no valves are positionedto control flow (a) between the chamber and the first passageway and (b)between the chamber and the second passageway.
 12. The system of claim10 wherein: the variable geometry seal is positioned to radiallyreciprocate, upon rotation of the rotor, between a retracted positionand an extended position in which the variable geometry seal extendsradially into the pressure-modifying chamber; the variable geometry sealcomprises a spring tending the variable geometry seal toward theextended position; and the variable geometry seal progresses toward theretracted position as a lobe of the rotor presses against the variablegeometry seal.
 13. The system of claim 10 wherein a first portion of thevariable geometry seal is fixedly coupled to the chamber housing and asecond portion of the variable geometry seal is circumferentiallymoveable relative to the chamber housing.
 14. The system of claim 10wherein the first port and the second port are positioned in a surfaceof the chamber housing that is generally parallel to the rotationalaxis.
 15. The system of claim 10, wherein: no valves are positioned tocontrol flow (a) between the chamber and the first passageway and (b)between the chamber and the second passageway; the rotor is alternatelyoperable in a first mode in which flow is provided from the secondpassageway to the first passageway via the chamber and in a second modein which flow is provided from the first passageway to the secondpassageway via the chamber; and the rotor and the variable geometry sealdivide the pressure-modifying chamber into a first chamber zone in fluidcommunication with the first passageway and a second chamber zone influid communication with the second passageway.
 16. The system of claim10, further comprising: a controller coupled to the shaft, wherein thecontroller is operable to redirect the rotor between operation in thefirst mode and the second mode by reversing a rotation direction of theshaft; and at least one of a motor, a generator, or a combinedmotor/generator coupled to the shaft.
 17. A rotary displacement systemcomprising: a chamber housing having a pressure-modifying chamber with afirst port and a second port; a first passageway in fluid communicationwith the chamber via the first port; a second passageway in fluidcommunication with the chamber via the second port; a shaft positionedwithin the chamber housing and rotatable relative to the chamber housingabout a rotational axis; a rotor positioned within thepressure-modifying chamber and comprising no more than two lobes,wherein the rotor is carried by and rotatable relative to the shaft, andwherein the rotor is alternately operable in a first mode in which flowis provided from the second passageway to the first passageway via thechamber and in a second mode in which flow is provided from the firstpassageway to the second passageway via the chamber; a fluid storagevolume in fluid communication with the pressure-modifying chamber viathe first and second passageways; and a controller coupled to the shaft,the controller being programmed with instructions that, when executed,reverse a rotation direction of the shaft.
 18. The system of claim 17,further comprising a seal positioned between the first port and thesecond port and having a varying radial extent to sealably contact thelobes of the rotor as the rotor rotates, wherein the seal and the rotorform a number of zones within the pressure-modifying chamber equal tothe number of lobes plus one.
 19. (canceled)
 20. The system of claim 17wherein no valves are positioned to control flow (a) between the chamberand the first passageway and (b) between the chamber and the secondpassageway.
 21. The system of claim 17, further comprising at least oneof a motor, a generator, or a combined motor/generator coupled to theshaft.
 22. The system of claim 17 wherein the fluid storage volumecomprises a geological formation, an underwater storage vessel, or ahigh-pressure tank.
 23. The system of claim 17 wherein the controllerfurther includes instructions that, when executed, reverse a rotationdirection of the shaft based at least in part on a first inputcorresponding to an energy supply level and a second input correspondingto an energy demand level. 24-104. (canceled)